The present invention concerns an arrangement and a method for the electrical control of the intensity of non-polarized light, a polarizing beam splitter being acted upon by the light to be controlled via an input face such that the light is split into two polarized light bundles that are orthogonal with respect to each other.
For a multiplicity of applications in the area of optics, for example in information-processing, in laser technology, and for many geodetic, astronomical, and navigational applications, arrangements are required which can switch light, carry out switchovers between optical channels, or modulate.
In known electro-optical switches and modulators of this type, either optically effective solid-body crystals or liquid crystals are used. Transparent crystals, such as can be manufactured from LiNbO3, require high working voltages, permit only small apertures, and are cost intensive. On account of the small permissible light bundle diameters, they are little suited for switching light bundles that contain images. As a consequence of the high dispersion that is inherent in them, the use of monochromatic light sources (lasers) is also necessary. The optical and electrical parameters change during use and thus impair the properties of the electro-optical switch or modulator. In addition, half of the light is lost, since these switches and modulators are employed in connection with polarizers.
In optical modulators that are improved with respect to these properties, modulators that have become known through German Published Patent Application No. 30 13 498 and British Patent No. 2046937 both polarization directions are used in connection with a polarizing beam splitter. However, the other cited disadvantages remain. Furthermore, it is disadvantageous in the known modulator that they require a working voltage of over 100 volts. In addition, significant costs arise as a result of a necessary cascading of the modulator.
In a further known arrangement, which was described by Hirabayashi, T. Kurokawa in "Liquid Crystal Devices for Optical Communication and Information-processing Systems," Liquid Crystals, Volume 14, pp. 307-317 (1993), a nematic liquid crystal is used in a so-called twist arrangement. In this context, larger apertures can be achieved. However, in nematic liquid crystals, their great switching times of, for example, several 100 milliseconds and problems in the representation of intermediate values are disadvantageous. Through Chiung-Shevy Wu, Shine Tsou Wu: "New Liquid Crystal Operation Modes," Volume 2949 SPIE, Image Sciences and Display Technologies, Proceedings Berlin Conference, FRG, 7-10 (1996), a modulator has become known in which the two polarization states s and p, generated by a polarizing beam splitter, are conveyed in the reverse direction by electro-optical liquid crystal cell. This leads to high rotation angles. However, the cells having a switching frequency of roughly 10 Hz are too slow.
From German Published Patent Application No. 196 31 644 (corresponding to PCT Publication No. WO 98/06002), an arrangement is known for switching optical patterns, which has a high switching efficiency and using which non-polarized, polychromatic light can be switched sufficiently rapidly. The arrangement, however, is very complicated and expensive, since it requires a multiplicity of liquid crystal cells in order to reduce the switching times. It is too expensive for wide use.